Back-side illuminated pixel

Abstract

A back-side illuminated pixel including a semiconductor substrate of a first conductivity type coated, on the front side of the pixel, with a three-layer assembly successively including a first layer of the second conductivity type, an insulating layer, and a second semiconductor layer. The three-layer assembly is interrupted in a central portion of the pixel by a transfer region of the first conductivity type laterally delimited by an insulated conductive wall extending from the front surface, Transistors are formed in the second semiconductor layer.

What is claimed is: 
     
       1. A device, comprising:
 a back side illuminated pixel, including:
 a semiconductor substrate of a first conductivity type; 
 a stack that includes:
 a semiconductor region of a second conductivity type formed in the substrate; 
 an insulating layer; and 
 a semiconductor layer, the insulating layer being positioned between the semiconductor region and the semiconductor layer; 
 
 a transfer region of the first conductivity type between first and second portions of the stack that each include the semiconductor region, insulating layer, and semiconductor layer, the transfer region being in a central portion of the back side illuminated pixel; 
 transistors formed in the semiconductor layer; 
 a first wall delimiting the semiconductor substrate laterally, the first wall extending from a front side of the semiconductor substrate to a back side of the semiconductor substrate; and 
 a filter on the back side of the semiconductor substrate and on an edge of the first wall. 
 
 
     
     
       2. The device of  claim 1 , comprising a second wall that laterally delimits the transfer region and is positioned between the transfer region and the semiconductor region, insulating layer, and semiconductor layer. 
     
     
       3. The device of  claim 2  wherein the second wall comprises a conductive material and an insulator bordering the conductive material. 
     
     
       4. The device of  claim 3  wherein the second wall is configured to be connected to a first potential and allow a charge transfer through the transfer region when connected to the first potential, and is configured block the charge transfer through the transfer region when connected to a second potential. 
     
     
       5. The device of  claim 2  wherein the second wall extends from the front side of the semiconductor substrate to an end of the transfer region. 
     
     
       6. The device of  claim 1  wherein the transfer region comprises an extension of the semiconductor substrate and a heavily-doped region of the first conductivity type. 
     
     
       7. The device of  claim 6  wherein the first wall comprises a conductive material and an insulator bordering the conductive material. 
     
     
       8. The device of  claim 1 , further comprising a contact formed on the semiconductor region. 
     
     
       9. The device of  claim 1 , further comprising a heavily-doped semiconductor layer of the second conductivity type between the back side of the substrate and the filter. 
     
     
       10. A method, comprising:
 manufacturing a pixel, the manufacturing including:
 forming, at a front side of a semiconductor substrate of a first conductivity type, a semiconductor region of the second conductivity type, the semiconductor substrate being part of a structure that includes an insulation layer on the semiconductor substrate and a semiconductor layer on the insulating layer, the insulating layer being positioned between the semiconductor region and the semiconductor layer, the forming the semiconductor region including:
 masking a central region of the structure; and 
 doping the substrate to form the semiconductor region extending under the insulating layer while the central region is masked; 
 
 forming a transfer region of the first conductivity type interrupting the semiconductor region, insulating layer, and semiconductor layer in a central portion of the pixel; 
 forming transistors in the semiconductor layer; 
 forming a first wall delimiting the semiconductor substrate laterally, the first wall extending from the front side of the semiconductor substrate to a back side of the semiconductor substrate; and 
 forming a filter on the back side of the semiconductor substrate and on an edge of the first wall. 
 
 
     
     
       11. The method of  claim 10  wherein manufacturing the pixel includes:
 forming a second wall extending from the front side of the semiconductor substrate completely through the semiconductor region, the insulating layer, and the semiconductor layer, the second wall delimiting the transfer region. 
 
     
     
       12. The method of  claim 11  wherein forming the transfer region includes:
 removing by etching central portions of the semiconductor layer and the insulating layer; and 
 doping an upper portion of the substrate in the central region of the structure to a higher doping level than a doping level of an underlying portion of the substrate in the central region. 
 
     
     
       13. The method of  claim 10  wherein manufacturing the pixel includes:
 forming interconnection levels on an upper surface of the semiconductor layer; 
 attaching a handle above the interconnection levels; and 
 thinning a back side the substrate. 
 
     
     
       14. An image sensor, comprising:
 a semiconductor substrate of a first conductivity type; and 
 a plurality of pixels, each pixel including:
 a semiconductor region of a second conductivity type; 
 an insulating layer; 
 a semiconductor layer, the insulating layer being positioned between the semiconductor region and the semiconductor layer, the semiconductor region, insulating layer, and semiconductor layer being orientated vertically with respect to each other; 
 a transfer region of the first conductivity type in a central portion of the pixel, the semiconductor region, insulating layer, and semiconductor layer completely laterally surrounding the transfer region; 
 transistors formed in the semiconductor layer; 
 a first wall through the semiconductor substrate delimiting a first lateral side of the pixel; 
 a second wall through the semiconductor substrate delimiting a second lateral side of the pixel; and 
 a filter on a back side of the semiconductor substrate and on respective edges of the first and second walls. 
 
 
     
     
       15. The image sensor of  claim 14 , wherein each pixel includes:
 an insulating structure that laterally delimits the transfer region of the pixel from the semiconductor region, insulating layer, and semiconductor layer of the pixel. 
 
     
     
       16. The image sensor of  claim 15  wherein the insulating structure includes an insulator surrounding a conductive layer. 
     
     
       17. The image sensor of  claim 15  wherein, in each pixel, the first semiconductor layer, the insulating layer, and the second semiconductor layer each directly contact the insulating structure of the pixel. 
     
     
       18. The image sensor of  claim 14  wherein each transfer region comprises an extension of the substrate and a heavily-doped region of the first conductivity type. 
     
     
       19. The image sensor of  claim 14  wherein each of the first and second walls includes an insulator surrounding a conductive layer. 
     
     
       20. A method, comprising:
 manufacturing a pixel, the manufacturing including:
 forming, at a front side of a semiconductor substrate of a first conductivity type, a semiconductor region of a second conductivity type, the semiconductor substrate being part of a structure that includes an insulating layer on the semiconductor substrate and a semiconductor layer on the insulating layer, the insulating layer being positioned between the semiconductor region and the semiconductor layer; 
 forming a transfer region of the first conductivity type interrupting the semiconductor region, insulating layer, and semiconductor layer in a central portion of the pixel, the forming the transfer region including:
 removing by etching central portions of the semiconductor layer and the insulating layer; and 
 doping an upper portion of the substrate in the central region of the structure to a higher doping level than a doping level of an underlying portion of the substrate in the central region; 
 
 forming transistors in the semiconductor layer; 
 forming a first wall delimiting the semiconductor substrate laterally, the first wall extending from the front side of the semiconductor substrate to a back side of the semiconductor substrate; and 
 forming a filter on the back side of the semiconductor substrate and on an edge of the first wall. 
 
 
     
     
       21. The method of  claim 20  wherein manufacturing the pixel includes:
 forming a second wall extending from the front side of the semiconductor substrate completely through the semiconductor region, the insulating layer, and the semiconductor layer, the second wall delimiting the transfer region.